The Greenland Ice Sheet meets the sea in this picture by Eric Rignot of NASA’s Jet Propulsion Laboratory.

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Melting of ice sheets in Antarctica and Greenland is accelerating, according to a new study to be published this month in Geophysical Research Letters. According to the research, this acceleration is three times faster than what is being observed for mountain glaciers and ice caps.

From the study:

The magnitude of the acceleration suggests that ice sheets will be the dominant contributors to sea level rise in forthcoming decades, and will likely exceed the IPCC projections for the contribution of ice sheets to sea level rise in the 21st century.

According to the new research, if melting of ice sheets continues at the current rate for the next 40 years, sea level rise from that source alone would equal 15 centimeters, or 5.9 inches by the year 2050. With ice loss from glaciers, ice caps and thermal expansion of the oceans also factored in, sea level could come up by a total of 32 centimeters, or 12.6 inches, by mid-century, according to the new research.

There is a caveat:

The researchers say there are significant uncertainties inherent in their projections. Of course, that could well mean greater sea level rise than they project in their paper. In fact, with new research over the years, scientists have repeatedly had to revise their estimates of sea level rise upward.

The last assessment report of the Intergovernmental Panel on Climate Change is a case in point. Published in 2007, it said we could get up to 59 centimeters of sea level rise by 2100. But that prediction did not include growing understanding of ice dynamics in Greenland. As a result, researchers have since estimated that sea level rise could exceed 1 meter by the end of the century. (For more information about this, see my post, “Mass Loss from Greenland Ice Sheet Accelerates,” from back in October.)

Even 1 meter of sea level rise would pose a major challenge. To offer one example, with a storm surge from a hurricane, New York City could actually be looking at 1.5 meters of water sloshing ashore. And that could flood a good portion of the city.

In the graphic at left, from the new research to be published in GRL, the the amount of ice lost from the Greenland and Antarctic ice sheets combined is plotted for the years 1992 through 2009. The graph is based on two independent measurement techniques, and the downward trend is clear.

So is the agreement between the two techniques. The first involved monitoring of ice sheets by synthetic aperture radar to determine ice loss, as well as climate modeling to determine additions to the ice sheets. The second used data from the Gravity Recovery and Climate Experiment (Grace) satellites. These spacecraft actually detect tiny changes in Earth’s gravity caused by alterations in the distribution of mass on our planet — including the movement of ice.

“These are two totally independent techniques, so it is a major achievement that the results agree so well,” co-author Isabella Velicogna of NASA’s Jet Propulsion Laboratory is quoted as saying in an American Geophysical Union press release, issued today.

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That trend looks perhaps not so linear, especially given what we know happened in 2010. I’ll ask Tamino to have a look.

So OK, another big deal paper. This is one of maybe a half dozen really important papers from the last few months (quite an impressive list, actually), nary a one of which got above the fold at the NYT, and I’ll bet this one won’t either. I have become quite convinced after thinking about it quite hard for the last few months that the “deficit model” is quite correct, but has little to do with the content of the stories and almost everything to do with their frequency and placement. IOW, if this story ends up on A8 or whatever, there’s a message implicit in that, and it’s the main one that readers will take away with them: This stuff must not be very important. In the meantime, that Alan Simpson must be one very, very important plains ape.

And the next day’s coverage is predictably thin. I didn’t read everything, but as far as I could see not one journalist picked up on the point that the straight extraploation to a 56 cm ice sheet contribution to SLR by 2100 might just be very, very conservative. The key issue of further commitment to melt beyond that date also didn’t get a mention as far as I could see.

If you haven’t, you might want to read Hansen and Sato (2011) on the subject, Tom. The upshot is that based on a close examination of ice sheet behavior during interglacials that got slightly warmer than at present, a fast collapse cannot be ruled out. Present data (from the timing Hansen and Sato probably hadn’t seen the Rignot paper) is consistent with a melt doubling time of ten years, which if it’s indeed happening would mean that fast collapse has started.

A certain degree of provincialism has come home to roost. The OMG expressions won’t happen in the US until cities begin to be inundated at the end of the century. Meanwhile, whole swaths of the nations of people of color who are impoverished and already hungry will slowly be swallowed by the rise of mere centimeters. The “Oh dear’s” will be said, but no subsequent change in behavior will be manifest by the worst of the polluters and energy users.

Gareth: Good catch! I thought I had checked all instances of Eric’s name, but evidently I missed that one.

Steve: Concerning the point that journalists generally didn’t say that sea level rise could be significantly greater than a straight extrapolation, I did. ;->

But I have been covering this topic for 30 years, so I’ve written enough ice sheet and sea level stories to know that over time, scientists have had to repeatedly raise their estimates of sea level rise upward. Journalists on deadline and with limited space may not immediately realize the importance of that context. And this is where better communication from scientists could come in.

“With the ice sheets disappearing more rapidly than previously thought, estimating the magnitude of future sea level rise is less important than acknowledging its quickening pace, Velicogna said. ‘The point is, it’s happening and we can’t deny it. Eventually it’s going to have an impact.’”

So here is a co-author of the study explicitly telling the journalist that the magnitude of future sea level rise is not as important as simply saying that it is now quickening. In my opinion, Velicogna should have discussed the broader context with Vastag. Maybe she did and he simply didn’t think it was important enough to put in the story. But somehow, I doubt that — especially given the specific words that Velicogna used here.

But at the end of the day, how much of a difference would that broader context have made in the minds of readers? The message of the story is that melting of ice sheets is accelerating, and sea level is likely going to rise higher than previously believed. I think that take-home message will stick in readers’ minds, whereas the actual number of centimeters of sea level rise by 2050 or 2100 will be forgotten before the reader even goes on to the next story.

So my point is that both journalists and scientists have the responsibility to provide the necessary context for stories like this. And not every story is going to be written by a journalist, like me, who has covered this topic for so damn long.

You’re absolutely right about the failure on the part of the scientists, Tom. Those strong statements needed to be in the press release and they weren’t; Velicogna’s verbal addition wasn’t the way to make the point. But couldn’t *somebody* covering this have connected to the big dot? Multiple-meter rise is possible this century, and that truly needed mentioning. I also think that some reference to the damage that will be done by high SLR needed to be there for readers to have a hook to hang their hats on. You did that nicely with the NYC example, and no one else did that I saw. But the larger problem remains the small amount of attention the story got.